1. Field of Invention
The present invention relates to an electron beam apparatus for irradiating a specimen to be inspected with an electron beam, and an inspection apparatus and inspection method for inspecting the specimen by the use of this electron beam apparatus.
2. Related Background Art
As is generally known, an electron beam apparatus for irradiating the specimen with an electron beam is equipped with an electron gun and electron optical system (electron lenses, etc.). In the electron beam apparatus, the electron beam discharged from the electron gun is applied on the specimen surface via the electron-optical system.
For an example of the equipment incorporating this electron beam apparatus, a description will be made on a scanning electron microscope (SEM) and electron beam inspection apparatus (EB inspection apparatus). By the way, to the SEM and EB inspection apparatus, a mechanism for detecting secondary electrons generated from the specimen by irradiating a specimen with an electron beam and creating a specimen image is incorporated.
To acquire the specimen image in SEM, the specimen is held stationary and the specimen surface is two-dimensionally scanned with the electron beam squeezed in the form of spot (spot beam). Consequently, SEM is popularly used for observing a comparatively small region (defect portion, etc.) of the specimen surface. The inspection of the whole specimen surface by SEM is not realistic due to its slow throughput.
As against this, the EB inspection apparatus has been under development in recent years in order to satisfy the requirements of inspecting a comparatively wide area or the whole area of the specimen surface.
For example, in the Japanese Patent Application Laid-Open (JP-A) No. 7-249393 or in the Japanese Patent Application Laid-Open (JP-A) No. 10-197462, there are disclosed EB inspection apparatus in which by scanning the specimen surface with the electron beam shaped in the form of a rectangle (rectangle beam) while the stage is being continuously moved, the specimen image is obtained.
In addition, in the Japanese Patent Application Laid-Open (JP-A) No. 10-294345, there is disclosed an EB inspection apparatus which acquires the specimen image by continuously moving the stage in one direction and allowing the spot beam to scan the specimen surface in the direction crossing at right angles the one direction mentioned above.
In these EB inspection apparatus, since the specimen image is acquired while the stage is being moved, the specimen image is able to be taken in continuously from a comparatively wide area or the whole area of the specimen surface. Consequently, the EB inspection apparatus is able to inspect the specimen surface at an incomparably higher speed than that of the whole surface inspection by SEM.
In addition, in the above-mentioned EB inspection apparatus, the inspection speed is able to be increased as much as the stage moving speed is increased.
Now, in the conventional EB inspection apparatus mentioned above, simply increasing the stage moving speed lowers the total current volume of electron beam irradiated over the specimen (hereinafter called the xe2x80x9cdosagexe2x80x9d) and the specimen image is degraded. In order to prevent this image degradation, the current volume of the electron beam discharged from the electron gun must be increased as much as the stage moving speed is increased. In this way, the high-speed inspection in the conventional EB inspection apparatus has been carried out by continuously irradiating the specimen surface with the large-current electron beam while the stage is being continuously moved at a high speed.
However, even during the high-speed inspection, the stage may be stopped or the moving speed may be decreased for some reason. If this kind of stage stop or speed reduction should occur during the high-speed inspection, the large-current electron beam continued to strike against the same place or the vicinity of the specimen surface, and the dosage rapidly increases at the relevant place.
On the other hand, there is a limit of acceptable dosage for the specimen, and if the electron beam continues to be irradiated to the level exceeding the allowable range of the dosage, contamination or charge-up occurs in the specimen, or for the worst, the specimen may be destroyed.
This kind of problem occurs even when the scanning by the spot beam is stopped or decelerated in the EB inspection apparatus disclosed in the Japanese Patent Application Laid-Open (JP-A) No. 10-294345.
It is an object of the present invention to provide an electron beam apparatus, inspection apparatus, and inspection method that can prevent a rapid increase of dosage caused by stop or deceleration of the relative move and can protect the specimen when the specimen is irradiated with the electron beam while the specimen and the electron beam are being relatively moved.
An electron beam apparatus according to the present invention is an electron beam apparatus for irradiating a specimen to be inspected with the electron beam comprising an electron beam outputting means for outputting the electron beam, a measuring means for measuring the dosage of electron beam irradiated per unit area of the specimen, a storage section for storing the predetermined dosage per unit area for the specimen, a detection means for detecting over exposure of the electron beam when the dosage per unit area measured by the measuring means is greater than the dosage per unit area stored in the storage section, and a control means for controlling the electron beam outputting means to reduce the dosage per unit area of the electron beam than the dosage per unit area stored in the storage section, when the over exposure of electron beam is detected by the detection means.
When the dosage of electron beam irradiated per unit area of the specimen is measured by the measuring means and the measured dosage is detected to be larger than the dosage stored in advance in the storage section in this way, the electron beam outputting means is controlled to reduce the dosage than that stored in the storage section. By this, when the specimen is irradiated with the electron beam while the electron beam irradiating position and the specimen position are relatively moved, the dosage of the electron beam to be applied to the specimen is able to be held to a predetermined dosage range stored in the storage section.
In addition, in the electron beam apparatus, the control means desirably controls to make the dosage of electron beam per unit area smaller than the dosage per unit area stored in the storage section when the over exposure of electron beam is detected over a specified time.
In the electron beam apparatus, the control means controls the electron beam outputting means in such a manner to make the dosage per unit area of the electron beam applied to the specimen smaller than the dosage per unit area stored in the storage section by expanding the irradiation range of the electron beam.
Furthermore, the electron beam apparatus may further comprise a stage for placing the specimen and a moving means for moving the stage, and may be characterized in that the measuring means measures the dosage per unit area in accordance with the output current volume of electron beam and the moving speed of the stage moved by the moving means.
Because the irradiation current volume of the electron beam applied to the specimen placed on a stage has a specified relation with the output current volume of the electron beam, the dosage per unit area is able to be measured in accordance with the output current volume of the electron beam and the stage moving speed.
In the electron beam apparatus, the measuring means may be measure the dosage per unit area in accordance with the secondary beam volume generated from the specimen.
Because the volume of the secondary beam generated from the specimen is defined in accordance with the volume of the electron beam impinging on the specimen, the dosage is able to be measured by the volume of the secondary beam.
The electron beam apparatus according to the present invention comprises an electron beam output means for outputting the electron beam, a stage irradiated with the electron beam outputted by the electron beam outputting means, a moving means for moving the stage, a storage section for storing the stage moving speed predetermined in accordance with the specimen and the output current volume of the electron beam, a detection means for detecting over exposure of the electron beam when the moving speed of the stage moved by the moving means is smaller than the moving speed stored in the storage section, and a control means for controlling the electron beam outputting means to prevent the stage from being irradiated with the electron beam when the over exposure of electron beam is detected by the detection means.
In this way, when the stage moving speed by the moving means is compared with the predetermined moving speed stored in the storage section and if the actual stage moving speed is smaller than the moving speed stored in the storage section, the over exposure of electron beam is detected. And when the over exposure of electron beam is detected, the control means controls the electron beam not to be applied to the stage, thereby quickly detecting the over exposure of the electron beam and stopping the electron beam from being irradiated over the stage.
The electron beam apparatus according to the present invention is an electron beam apparatus for irradiating the specimen to be inspected with the electron beam, and comprises an electron beam outputting means for outputting the electron beam, a storage section for storing the output current volume of the electron beam and the volume of the secondary beam predetermined in accordance with the specimen and the output current volume of the electron beam, a detection means for detecting the over exposure of the electron beam when the volume of the secondary beam generated from the specimen is greater than the volume of the secondary beam stored in the storage section, and a control means for controlling the electron beam outputting means to prevent the stage from being irradiated with the electron beam when the over exposure of the electron beam is detected by the detection means.
The volume of the secondary beam generated from the specimen in this way is compared with the volume of the secondary beam stored in the storage section, and when the volume of the generated secondary beam is greater than the volume of the secondary beam stored in the storage section, the over exposure of the electron beam is detected. And when the over exposure of the electron beam is detected, the control means controls the electron beam from being applied to the stage, thereby quickly detecting the over exposure of the electron beam and preventing the electron beam from being applied to the stage.
The inspection apparatus according to the present invention comprises the electron beam apparatus and an image acquisition means for acquiring the image information of the specimen in accordance with the secondary beam generated from the specimen.
By configuring an inspection apparatus equipped with an electron beam apparatus, it is possible to prevent the condition in which the specimen to be inspected is destroyed by over exposure of the electron beam.
In addition, in the inspection apparatus, the measuring means may be intended to measure the dosage on the basis of the output current volume of the electron beam and the contrast ratio of the image information acquired by the image acquisition means.
Because the contrast ratio of the image information formed on the basis of the secondary beam is determined by the dosage of the electron beam impinged in the specimen, the dosage can be measured by the contrast ratio of the image information.
In addition, the inspection apparatus according to the present invention is an inspection apparatus for inspecting the specimen by irradiating the specimen to be inspected with the electron beam, comprises an electron beam outputting means for outputting the electron beam and irradiating the specimen with the electron beam, a storage section for storing the contrast ratio predetermined on the basis of the specimen and the output current volume of the electron beam, a detection means for detecting the over exposure of the electron beam when the contrast ratio of the image information acquired by the image acquisition means is greater than the contrast ratio stored in the storage section, and a control means for controlling the electron beam outputting means to prevent the electron beam from being applied to the specimen.
In this way, the contrast ratio of the image information based on the secondary beam generated from the specimen is compared with the contrast ratio of the image information predetermined and stored in the storage section, and when the contrast ratio of the image information based on the secondary beam actually generated is greater than the contrast ratio of the image information stored in the storage section, the over exposure of the electron beam is detected. And when the over exposure of the electron beam is detected, the control means controls the electron beam from being applied to the specimen to quickly detect the over exposure of the electron beam and stops electron beam from being applied to the specimen.
The inspection method according to the present invention is an inspection method for inspecting the specimen by irradiating the specimen to be inspected with the electron beam and comprises an electron beam irradiation step for outputting the electron beam and irradiating the specimen with the electron beam, an image acquisition step for acquiring the image information of the specimen based on the secondary beam generated from the specimen, a measuring step for measuring the dosage of the electron beam irradiated per unit area of the specimen, a detection step for detecting the over exposure of the electron beam when the dosage per unit area measured in the measuring step is greater than the dosage per unit area predetermined for the specimen, and a control step for controlling the electron beam outputting means in such a manner that the dosage per unit area of the electron beam is made smaller than the dosage per unit area stored in the storage section when the over exposure of the electron beam is detected in the detection step.
The dosage of the electron beam irradiated per unit area of the specimen is measured in this way, and the measured dosage and the dosage stored in the storage section predetermined are compared to detect the over exposure of the electron beam. And because the dosage is brought to be reduced when the over exposure of the electron beam is detected, it is possible to prevent the condition in which the specimen to be inspected is not destroyed by the electron beam.
The inspection method according to the present invention is an inspection method for inspecting the specimen by irradiating the specimen to be inspected with the electron beam, and comprises an electron beam irradiating step for outputting the electron beam to irradiate the specimen with the electron beam, an image acquisition step for acquiring the image information of the specimen based on the secondary beam generated from the specimen, a stage moving step for moving the stage with the specimen placed, and a detection step for detecting the over exposure of the electron beam when the moving speed of the stage moved in the stage moving step is smaller than the stage moving speed predetermined in accordance with the specimen and the output current volume of the electron beam, and a control step for controlling the electron beam to prevent the stage from being irradiated with the electron beam when the stage is detected to be overexposed with the electron beam in the detection step.
In this way, when the stage moving speed is compared with the moving speed predetermined and stored in the storage section and the moving speed of the actual stage is smaller than the moving speed stored in the storage section, the over exposure of the electron beam is detected. And when the over exposure of the electron beam is detected, control is made to prevent the stage from being irradiated with the electron beam in the control step. With this contrivance, the over exposure of the electron beam is quickly detected and it is able to stop the stage from being irradiated with the electron beam.
The present invention will be more fully understood from the detailed description given hereinbelow and the accompanying drawings, which are given by way of illustration only and are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will be apparent to those skilled in the art from this detailed description.